A method for sterilizing a packaging container is provided which satisfies energy-saving requirements with consideration for energy cost and initial cost, which has high sterilization performance, and which is employable to make a highly safe dry sterilization system. The method for sterilizing a packaging container comprises: (a) a step of jetting a hydrogen peroxide-containing gas at a temperature of 10 to 60°C, preferably 10°C to 40°C, and at a concentration of 10 to 200 ppm (for example, an unsaturated hydrogen peroxide-containing gas that is obtained by supplying air into a gas-phase portion in a tank reserving hydrogen peroxide solution at a concentration of 3 to 40%) into a packaging container to be sterilized to bring hydrogen peroxide into contact with an inner surface of the packaging container (b) a step of irradiating the inner surface of the packaging container with ultraviolet radiation and (c) a purging step of jetting sterile air at a temperature of 10 to 60°C, preferably at room temperature, into the packaging container to replace the hydrogen peroxide-containing gas in the packaging container with the sterile air.
